Deflecting circuit



Patented Jan. 17, 1939 v I I UNITED "STATES PATENT 'oFFi DEFLECTING'omoorr Arthur W. Vance, Philadelphia, Pa., assignor, by mesneassignments, to Radio Corporation of America, New York, N. Y., acorporation of Delaware Application October 31, 1934, Serial No. 750,908

7 Claims. (01. 250-36) My invention relates to deflecting circuits forcircuit I! through a coupling capacitor l9. The cathode-ray tubes andparticularly to television synchronizing signals consist of horizontalsyndeflecting circuits which are operated in synchronizing impulseswhich occur at the end of chronism with controlling or synchronizingimeach scanning line and of framing impulses pulses. which occur at theend of each picture frame.

An object of my invention is to provide an The separating circuit I'Iseparates the picture improved deflecting circuit which iscomparativesignals from synchronizing signals, and the horily low incost. zontal synchronizing impulses from the vertical A further objectof my invention is to provide framing impulses. 10 a simplifieddeflecting circuit which will produce The vertical framing impulses areimpressed 10 a voltage of the desired waveform and which through acoupling capacitor 2| upon a vertical may be synchronized readily with acontrolling deflecting circuit 23 which produces a flow of signal.saw-tooth current through the deflecting coils A still further object ofmy invention is to H in synchronism with the framing impulses. providean improved deflecting circuit which will The horizontal synchronizingimpulses are im- 15 produce a voltage wave containing a saw-toothpressed through a coupling capacitor 25 upon a component and a largeimpulse component. horizontal deflecting circuit designed in accord- Inthe preferred embodiment of my invention, ance with a preferredembodiment of my invenan electric discharge tube is so connected withtion. One unit of the horizontal deflecting circuit associated circuitelements that it oscillates to is an oscillator 27 of the type describedand 20 produce substantially square-top voltage imclaimed in mycopending application, Serial No. pulses periodically. These impulsesare im- 718,353, filed March 31, 1934, and assigned to the pressed upona resistor and a-capacitor which Radio Corporation of America. Thisoscillator are connected in series, the resistor having a comprises anelectric discharge tube 29 such as comparatively high resistance value.Voltage a vacuum tube having a cathode 3!, a control 25 appearing acrossa portion of the resistor-capacigrid 33 and a plate 35. The plate 35 issupplied tor combination is applied to a second electric with positivepotential from a suitable source discharge tube which supplies either asaw-tooth such as a battery 31 through the primary windcurrent or asaw-tooth voltage to a cathode-ray ing 39 of a transformer 41. Thecontrol grid 33 p tube deflecting device. is connected through thesecondary winding 43 30 Other objects, features and advantages of my ofthe transformer Alto the cathode 3| whereby invention will appear fromthe following descripthe plate and grid circuits of the vacuum tube tiontaken in connection with the accompanying 29 are inductively coupled.

drawing, in which- As explained, in the above mentioned copend- 35Figure 1 is a circuit diagram of a television ing application, the plateand grid circuits of the 35 receiver embodying my invention, and tube 29are coupled in such phase that as the Fig. 2 is a circuit diagramillustrating another flow of plate current through the primarywindembodiment of my invention. ing 39 increases, a positive voltage isapplied to In Fig. 1, my improved deflecting circuit is the control grid33 through the transformer 4|.

40 shown applied to a television receiver which in- The plate currentincreases until saturation is 40 cludes a radio receiver I, a pictureamplifier 3 reached, at which time a negative voltage is imandacathode-ray receiver tube 5. The cathodepressed upon the control grid33 through the ray tube 5 comprises an evacuated envelope havtransformer4! whereby the tube 29 is rapidly ing a fluorescent screen I at one endand an driven beyond the cut-off point. As a result of 4,5 electron gun9 at the other end for producing this action, negative voltage impulsesof the charan electron beam. acter indicated by the curve 45 areproduced Suitable deflecting devices, such as deflecting across thesecondary winding 43. coils II and i3, are provided for deflecting theIn practice it has been found that in order electron beam vertically andhorizontally, reto produce a substantially perfect saw-toothourspectively, for scanning the fluorescent screen 1. rent flow througha deflecting coil, the voltage 50 The output of the picture amplifier 3includes impressed upon the deflecting coil circuit must both picturesignals and synchronizing signals, contain a saw-tooth component inaddition to all these signals being impressed upon the con thesquare-top impulse component, this being trol grid of the cathode-raytube 5 through a necessary since the deflecting coil circuit is notcoupling capacitor [5 and upon a separating purely inductive. In orderto produce such a 55 composite voltage wave, I provide a resistor 41having a comparatively high resistance value and a capacitor 49connected in series. The secondary winding 43 of the transformer isconnected across this resistor-capacitor combination, the connection tothe resistor 4'! being through a slidable contact point 5|. By varyingthe position of the contact point 5| the magnitude of the electron beamdeflection may be varied as will be apparent from the followingdescription.

The impedance of the resistor 41 is so high that the flow of currentthrough the capacitor 49 produced by the square top voltage impulses 45is substantially independent of the voltage built up across thecapacitor 49 as it becomes charged. Therefore, the flow of currentthrough the capacitor 49 and resistor 41 has substantially the same waveform as the voltage as indicated by the curve 0. The voltage appearingacross the capacitor 49 will have a saw-tooth wave form as indicated bythe curve e'e. The voltage appearing across the resistor 41 will havethe form indicated by the curve ir, er. It will 'be apparent that thedesired composite wave form for producing a flow of saw-tooth currentthrough a deflecting coil may be obtained by adding the saw-toothvoltage appearing across the capacitor 49 to the square-top voltageimpulse appearlng across a portion 01' the resistor 41.

The composite voltage wave is impressed upon the input terminals of anelectric discharge tube 53 which preferably is a vacuum tube having alow plate impedance, As illustrated, the tube is a vacuum tubecomprising a cathode 55 a control gride 51 and a plate 59. The controlgrid 51 is connected through a slidable contact point 6| to the resistor41. The cathode 55 is con nected through a self-biasing resistor 63 tothe lower end of the capacitor 49, the self-biasing resistor beingprovided with the usual by-pass capacitor 65. r

The plate 59 of the vacuum tube 53 is supplied with a positive potentialfrom a suitable source, such as a battery 61, through an inductance coil69. One terminal of the deflecting coils I3 is connected to the plate 59through a conductor H and a blocking capacitor 13, while the otherterminal of the coils I3 is connected tothe cathode 55 through aconductor 15. A resistor TI is provided which may be connected acrossthe deflecting coils l3 by means of a switch 19 for a purpose which willbe described hereinafter.

An important characteristic of my improved deflecting circuit is thatthe impulse component of the voltage wave applied to the deflectingcoils may be much larger than the voltage of any battery or anotherpower supply. For this reason my circuit is especially valuable where itis desired to employ a low plate impedance output tube such as the oneillustrated. It will be understood that because of its low plateimpedance, such a tube requires only a small saw-tooth component in thevoltage impressed upon its input electrodes.

It may be noted that there are several advantages in employing an outputtube having a low plate impedance, One advantage is that because of thesmall saw-tooth voltage component required, any imperfection in thissaw-tooth component has comparatively little effect on the shape of thedeflecting current wave form. Therefore, with a low impedance tube it iseasier to obtain a good saw-tooth current in the deflecting coils.

A further advantage in the use of a low impedance output tube is pointedout in my copending application, Serial No. 741,230, filed August 24,1934, and assigned to RCA Victor Company, Inc. In the said applicationit is shown how a resistor, such as the resistor Tl, may be connectedacross the deflecting coils whereby energy stored in these coils will bedischarged through the resistor instead of through the Vacuum tubeduring the return line period. This makes it possible to obtain agreater deflection with a given size vacuum tube by increasing the platevoltage and, at the same time, increasing the number of turns on thedeflecting coils. With the circuit operated in this manner, the platevoltage is raised considerably above the rated plate voltage with acorresponding increase in plate current, providing a low plate impedancetype of tube is employed. In the case of a screen grid tube, which has ahigh plate impedance, an increase in the plate voltage above the ratedvalue will not materiallyincrease the plate current output.

If the circuit is adjusted to operate with the deflecting coilsdischarging through a resistor, instead of through the vacuum tube, thepreferred adjustment is such that the impulse component of the voltageimpressed upon the grid of the output tube is great enough to drive thetube beyond the cut-off point.

My deflecting circuit is easily synchronized with the incomingsynchronizing impulses in the manner described in my above mentionedapplication, Serial No. 718,353. As stated in that application, theoscillator readily oscillates in synchronism with negative synchronizingimpulses applied to the control grid.

In Fig. 2, an embodiment of my invention is shown applied to a verticaldeflecting circuit. In this circuit a generator of square-top voltageimpulses is indicated at 8|. The squaretop impulses, similar to theimpulses 45, are impressed across a resistor 83 and a capacitor 85connected in series whereby a voltage wave having a sawtooth componentand an impulse component is produced which may be impressed upon avacuum tube indicated at 81. In this embodiment, the output tube 81 isshown as a pentode although it will be understood that a different typeof tube may be utilized if desired. Positive potential is applied to theplate of the tube 87 through a plate resistor 89 instead of through aninductance coil because of the difflculty in obtaining an inductancecoil having the desired high impedance at the low vertical deflectingfrequency.

The output circuit of the tube is coupled to the vertical deflectingcoils H. It may be noted that deflecting coils always have a certainamount of distributed capacity as indicated in dotted lines at 9|. Thiscauses certain undesired resonant efiects which are minimized by dampingthe resonant circuit. If a low impedance tube, such as illustrated inFig. 1, is employed as the output tube, its plate impedance may be lowenough to provide the necessary damping. In Fig. 2 the necessary dampingis provided by the plate resistor 89 which is efiectively shunted acrossthe deflecting coils Hand the distributed capacity.

While certain types of tubes and certain circuit values have beenindicated in Figs. 1 and 2, it Will be understood that these are merelygiven by way of example. The circuit values are indicated in ohms,micro-farads, henrys, and number of turns. Also, although only one formof impulse generator has been illustrated, it should be understood thatother forms may be substituted. For example, in a television transmitterdeflecting circuit, the vacuum tube oscillator 21 may be replaced by arotatable disc having openings therein through which a light beam passesto strike a photoelectric cell for the production of voltage impulses ina manner well known.

It will be apparent that various other modifications may be made in myinvention without departing from the spirit and scope thereof and Idesire, therefore, that only such limitations shall be imposed thereonas are necessitated by the prior art and set forth in the appendedclaims.

I claim as my invention:

1. In combination, means for producing substantially square-top voltageimpulses periodically, a resistor and a capacitor connected in series,means for impressing said impulses across said resistor-capacitorcombination, an electric discharge tube having an input circuit and anoutput circuit, means for appying the voltage drop appearing across saidcapacitor tosaid input circuit, and a utilization device coupled to saidoutput circuit, said resistor having such high impedance that the flowof current produced through said capacitor by said voltage impulses issubstantially independent of the voltage built up across said capacitor.

2. Apparatus according to claim 1 characterized in that said utilizationdevice is an inductance coil and further characterized in that, inaddition to the voltage drop across said capacitor, the voltageappearing across a portion of said resistor is applied to said inputcircuit.

3. Apparatus according to claim 1 characterized in that said tube is alow plate impedance tube of the three element type.

4. Apparatus according to claim 1 characterized in that said first meanscomprises an electric discharge tube having plate and grid circuitswhich are inductively coupled and which are non-resonant at thefrequency of occurrence of said impulses.

5. In combination, means for producing substantially square-top voltageimpulses periodically, a resistor and a capacitor connected in series,means for impressing said impulses across said resistor-capacitorcombination, a three element vacuum tube having an input circuit and anoutput circuit, said tube having a low plate impedance, inductance coilscoupled to said output circuit, and means for applying the voltageappearing across said capacitor and the voltage appearing across aportion of said resistor to said {input circuit, said resistor havingsuch high impedance that the flow of current produced through saidcapacitor by said voltage impulses is substantially independent of thevoltage built up across said capacitor.

6. Apparatus according to claim 5 characterized in that a resistorelement is shunted across said inductance coils, and furthercharacterized in that the voltage appearing across said resistor portionis of the proper polarity and magnitude to drive said tube beyondcut-off.

'7. In combination, means for producing substantially square-top voltageimpulses periodically, a resistor and a capacitor connected in series,and means for impressing said impulses across said resistor-capacitorcombination whereby a voltage having an impulse component and asaw-tooth component may be taken therefrom, said resistor having suchhigh impedance that the flow of current produced through said capacitorby said voltage impulses is substantially independent of the voltagebuilt up across said capacitor.

ARTHUR W. VANCE.

